Constant acceleration fluid energy mill

ABSTRACT

A fluid energy mill comprising a lower inlet section and an upper classification section connected by a vertical upstack on one side and a vertical downstack on the other side, the inlet section having tangential nozzles connected to a source of gaseous fluid pressure and a raw feed inlet, whereby the raw feed particles are entrained and centrifugally whirled around the mill by the pressure fluid. The portion of the inlet chamber adjacent the upstack, as well as the upstack itself and the portion of the classification chamber adjacent the upstack form part of an antifriction curve. The classification section is preferably generally circular and has at least one exhaust outlet in the center so that the lighter particles on the inner periphery of the centrifugal path are rotated in a helical path until exhausted through the outlet. Preferably, nozzles are provided in the classification section to project pressure fluid thereinto in a generally elliptical path.

United States Patent Stephanofi Mar. 14, 1972 [54] CONSTANT ACCELERATIONFLUID ENERGY MILL [72] Inventor: Nicholas N. Stephanol'f, Haverford, Pa.

[73] Assignee: Fluid Energy Processing & Equipment Co.,

Hatfield, Pa.

[22] Filed: Apr. 6, 1970 [211 App1.No.: 25,962

[52] US. Cl. ..24l/5, 241/39 [51 Int. Cl. ..B02c 19/06 [58] Field ofSearch ..24l/5, 39, 40, 41

[56] References Cited UNITED STATES PATENTS 2,590,220 3/1952 Stephanoff..241/5 X 3,229,918 1/1966 Trost 2,219,011 10/1940 Kidwell et 241/392,704,635 3/1955 Trost .24l/5 2,735,626 2/1956 Trost ..24 l/39 3,491,953l/1970 Stephanoff ..24l/39 3,539,294 11/1970 Hwang ..241/5 PrimaryExaminerGranville Y. Custer, Jr. Attorney-Arthur A. Jacobs [5 7]ABSTRACT A fluid energy mill comprising a lower inlet section and anupper classification section connected by a vertical upstack on one sideand a vertical downstack on the other side, the inlet section havingtangential nozzles connected to a source of gaseous fluid pressure and araw feed inlet, whereby the raw ,feed particles are entrained andcentrifugally whirled around the mill by the pressure fluid. The portionof the inlet chamber adjacent the upstack, as well as the upstack itselfand the portion of the classification chamber adjacent the upstack formpart of an antifriction curve. The classification section is preferablygenerally circular and has at least one exhaust outlet in the center sothat the lighter particles on the inner periphery of the centrifugalpath are rotated in a helical path until exhausted through the outlet.Preferably, nozzles are provided in the classification section toproject pressure fluid thereinto in a generally elliptical path.

9 Claims, 8 Drawing Figures PATENTEBHAR 14 I972 3. 648 936 INVENTORNICHOLAS N. STEPHANOFF ATTORNEY CONSTANT ACCELERATION FLUID ENERGY MILLThis invention relates to a fluid energy mill, and it particularlyrelates to an improved fluid energy mill wherein the acceleration of theparticles in the centrifugal path is better controlled and wherein theexhausting of the lighter particles from the mill is made more effectiveand efficient.

Fluid energy mills, as such, are now well-known and are in extensiveuse. Many of these mills comprise a vertically elongated generallyarcuate construction including straight, elongated upstack and downstacksections connected at top and bottom by arcuate elbow sections. Nozzleslead into the lower elbow portion from a source of gaseous fluid underpressure. These nozzles are tangentially directed relative to the pathof flow through the lower elbow, or inlet, section, and all or some ofthem may be so positioned that the fluid jets issuing therefromintersect each other, whereby a greater grinding or pulverizing effectis obtained. The inlet section is also provided with a feed inlet forthe solid pulverulent material being ground or otherwise treated; thisfeed inlet being so arranged that the feed path intersects the fluid jetstreams, so that the particles are entrained thereby and are not onlyground or otherwise treated by action of the fluid, but are alsocirculated through the mill by the tangentially directed fluid stream.

During the aforesaid type of action, the centrifugal force of thecirculating fluid and particles carries these particles into aclassification zone where they are centrifugally separated into smallerand larger particles, the smaller, lighter particles tending to remainon the inner periphery of the circulating stream while the larger,heavier particles tend to remain on the outer periphery. Thiscentrifugal separation is utilized to remove the lighter particles fromthe mill while recirculating the heavier particles for an additionalpass through the mill to effect further pulverization or other treatmentthereof. This is achieved by providing an exhaust duct on the innerperiphery of the mill adjacent the entrance to the return stack. As thecentrifugal action carries the particles past this exhaust duct, thelighter particles on the inner peripheral portion of the stream flowthrough the exhaust duct and are removed from the mill, while theheavier particles on the outer peripheral portion of the stream passback into the inlet section and, after being intermixed with additionalrow material, are again subjected to the pulverizing action of the fluidjet streams.

A problem in the above type of mill has always been the fact that theexhausting of the lighter particles has been somewhat inefflcientbecause a significant portion of these lighter particles was carrieddown with the heavier particles for further treatment. This not onlywasted energy on particles which were already sufficiently treated, buttended to over-pack the treating zone so that the heavier particles,which were being recycled, and the additional raw feed were notsufficiently treated.

Another disadvantage of prior fluid energy mills was inherent in theirconstruction whereby the particles moved from an arcuate treating zonethrough a substantially straight vertical upstack into an arcuateclassification zone. The sudden difference of curvature between thetreating zone and the upstack not only caused many of the particles tocontinue, on their momentum, to strike the walls of the upstack, therebycausing undue wear, but also resulted in a sudden loss of accelerationof the particles, whereby many fell, under the influence of gravity,back into the treating zone. The same wear effect resulted from thesudden change of curvature between the vertical upstack and theclassification zone.

In addition, the loss of centrifugal energy and acceleration as theparticles moved through the substantially straight, vertical upstackinterfered with the efficient separation of the lighter and heavierparticles in the classification zone.

It is, therefore, one object of the present invention to provide a fluidenergy mill which has an improved means for separation of lighter fromheavier particles and a more effective means for exhaustion of thelighter particles from the mill.

Another object of the present invention is to provide a fluid energymill which reduces wear on the interior surfaces of the mill and whichmore efiectively maintains a substantially constant deceleration andacceleration of the particles as they pass through the mill.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following description when read in conjunction with theaccompanying drawings wherein:

FIG. 1 is a sectional view of a mill embodying the present invention.

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1.

FIG. 3 is a sectional view taken on line 33 of FIG. 1.

FIG. 4 is a sectional view taken on line 4-4 of FIG. 1.

FIG. 5 is a fragmentary sectional view of a modified form of the millofFIG. 1.

FIG. 6 is a sectional view taken on line 6-6 of FIG. 5.

FIG. 7 is a fragmentary sectional view of an alternative embodiment ofthe present invention.

FIG. 8 is an illustration of the anti-friction curve used in theconstruction of the mill.

Referring now in greater detail to the various figures of the drawingswherein similar reference characters refer to similar parts, there isshown in FIG. 1 a mill, generally designated 10, comprising a lowerinlet section 12, an upstack 14, a classification section 16 and adownstack 18.

The inlet section 12 is arcuate in length conforming to the initialportion of the Tractrix or Schieles anti-friction curve. This curve isdescribed, for example, in The Mechanical Engineering Handbook; Kent;9th Ed; 1948; John Wiley & Sons, Inc.; page 50. This section is alsogenerally V-shaped in cross section (as best seen in FIG. 4), with theradially inner wall 20 being wider than the outer wall 22, the inner andouter walls being connected by inclined side walls 24 (as best shown inFIG. 4). A series of nozzles 26 are provided for the inlet section 12,these nozzles being preferably at varying inclined angles to the inletsection and being in fluid connection with a manifold 28 that isconnected to a source of gaseous fluid under pressure (not shown) bymeans of a conduit 30.

The upstack 14, which is integral with the inlet section 12, is providedwith a gradual curvature that is a continuation of the anti-frictioncurve ofthe inlet section 12. The curvature of the upstack 14 is suchthat particles being centrifugally whirled through the inlet section 12will continue on their centrifugal path without any significant numberof them striking either the inner or outer walls of the upstack.

In addition to having the aforesaid anti-friction curvature, the upstack14 has a generally V-shaped cross section wherein the inner wall 32 (asbest shown in FIG. 3) is wider than the outer wall 34 and is connectedthereto by inclined side walls 36. This configuration is a continuationof that of the inlet section 12.

The upstack l4 merges into the classification section 16 by means of theouter wall 38 of the classification section 16.

The classification section 16, in addition to being bounded by thearcuate outer wall 38, is also bounded by a reversably arcuate innerwall 40, the two arcuate walls forming a generally ellipticalclassification chamber.

At the center of the classification section 16 there is provided anexhaust opening 42 on each side. Each exhaust opening 42 mates with anexhaust duct 44 (as best seen in FIG. 2). Both ducts 44 may be connectedto a common exhaust manifold (not shown). In the lower wall 40 areprovided one or more (here shown as two) angular nozzles 46 which are soinclined as to project jets of gaseous fluid to follow the ellipticalpath formed by the classification section 16 around the exhaust openings42. These nozzles are connected to any desired source of gaseous fluidunder pressure. They are here illustrated as being connected to themanifold 28 by ducts 47. The nozzles 46, although preferably provided,are optional, and may be omitted, although such omission would preventthe most effective circulation within the classification section.

The downstack section 18 has a cross-sectional shape similar to that ofthe upstack section, whereby the outer wall 48 (as best seen in FIG. 3)is wider than the inner wall 50 and is connected thereto by inclinedside walls 52. However, it is not as wide as the upstack because lessspace is required for centrifugal acceleration and because only theheavier pass therethrough. I

The downstack 18, instead of having an anti-friction curvature, isvertically substantially straight. This is because separation hasalready taken place in the classification section and, since all theparticles passing through the downstack are heavy and are being returnedto the inlet section, the straight vertical drop takes advantage of theaction of gravity in increasing the acceleration of the downwardlymoving particles.

A feed inlet 54 leads into the inlet section 12 at the juncture of theinlet section with the downstack 18. This feed inlet is shown ascomprising a hopper 56 connected to a Venturi tube 58 and provided witha nozzle 60 connected through a valve 62 to a source of gaseous fluidunder pressure; whereby the gaseous fluid propels the particles from thehopper 56 through the Venturi tube 58, where they are accelerated, intothe mill. However, any other desirable type of feed means may besubstituted within the scope of the invention.

In operation, the raw pulverulent material is fed into the mill throughthe inlet 54 and is entrained by the gaseous fluid jets from nozzles 26.Since the nozzles 26 are at variable angles relative to each other, thejets intersect and increase the tendency of the particles to impactagainst each other and pulverize each other. At the same time, since thenozzles are so inclined that the general direction is to the left (asviewed in FIG. 1), the particles are centrifugally whirled into theupstack 14.

The anti-friction curvature prevents abrasion of the mill walls by theparticles and also acts in the upstack to decelerate the upward movementof the particles, so that movement of the largest particles in theupstack are retarded and these particles, therefore, drop back into theinlet chamber for further treatment.

As the particles and entraining gaseous fluid move into theclassification section 16, the curvature of the mill increases, therebyincreasing the acceleration of the particles and fluid. Thisacceleration is usually sufficient to cause the lighter particles torotate around the central openings 42 in a helical path until they passthrough the openings closest thereto. This action is aided by the factthat since the fluid exhausts through the center opening 42, the viscousdrag of the spiraling fluid overcomes the centrifugal force on thelighter particles and helps to carry them out through the opening 42. Atthe same time, the increased centrifugal force carries the heavierparticles around the outer periphery of the centrifugal path and downinto the downstack 18 where they are mixed with fresh material from theinlet 54 and pass into the inlet section 12 for further grinding.

The nozzles 46 are preferably used to further increase the centrifugalacceleration of the particles and fluid in the classification section,whereby the heavier particles are more thoroughly urged toward the outerperiphery while the lighter particles are given a greater rotationalacceleration to increase their helical movement toward the centralexhaust openings, thereby further classifying the mass of particles togive a still finer end product.

In FIGS. and 6 there is shown a modified form of the mill describedabove, wherein the mill, generally designated 100, is the same as thatof FIG. 1 except that in the classification section 102 there is atransverse rotatable open-ended tube 104 which extends laterally throughthe section 102. The tube 104 is provided with a slot 106 on itsunderside. The slot 106 is in communication with the chamber formed bythe classification section 102 and permits entrance into the tube 104 ofthe helically travelling lighter particles. The rotatability of the tube104 permits the slot 106 to be adjusted into any desirable position.

The construction of FIGS. 5 and 6 permits the helically travellingparticles to pass directly into the exhaust opening which is'in theirhelical path, instead of having to make a lateral turn in order to passinto the lateral openings 42 provided in the form of the mill shown inFIGS.1-4, thereby refining the end product.

In FIG. 7 there is shown an alternative form of the mill of FIG. 1wherein the mill, generally designated 200, has the same anti-frictioncurvature, such curvature being partially indicated at 202. However,instead of the elliptical classification section with a central opening,there is provided a classification section 204 which is an arcuatesection similar to the inlet section but having a generally V-shapedcross section reverse to that of the inlet section (not shown), thisinlet section having the same construction as the inlet section 12 inthe mill of FIGS. 14. The exhaust opening is provided at 206 in thestandard manner.

The gaseous fluid used is a matter of choice depending upon the materialbeing treated and the results desired. The fluid may, for example, beair, steam, an inert gas or vapor, or any other desirable and feasiblegas or vapor, the term gaseous fluid being generic to all gases andvapors. The gaseous jets may be ejected from the nozzles either underhigh velocities of the acoustic or super acoustic range, or lowervelocities, depending on whether a greater or lesser degree of grindingis desired, and also depending on the construction of the nozzles. Theparticular construction of the nozzles themselves is standard and may beof the so-called convergent-divergent type or the abrupt" type dependingon the velocities desired; the convergent-divergent type being of agenerally Venturi shape and providing higher velocities.

Although this apparatus has been described primarily for grinding orpulverizing, it may also be used for such other purposes as drying,chemical reactions, coating, agglommerating or deagglomerating, and manyother functions, depending on the type of gaseous fluids used, thematerials fed into the mill, the velocities and pressures of the gaseousfluids as they pass into the mill, the angles of incidence of thenozzles relative to the interior of the mill, etc. For example, if avery hot, low pressure gaseous fluid were used, there would be little orno grinding but only a drying of the particles, if wet. Such drying,itself, causes the formation of lighter and heavier particles because itremoves adherent liquid which acts as an adhesive between particles ofvarying sizes. In addition, the gaseous fluid may be of a type tochemically react with the treated material. Or particles of differentchemical composition may be simultaneously used whereby, upon impact,they may physically adhere or chemically combine.

It is to be further noted that although the mill is illustrated as beingvertical, this being the preferred position, it may also be utilized inthe horizontal or any other desired position.

The material being treated may be either pulverulent solid material, aliquid slurry or even a liquid wherein the liquid may be broken up intoliquid particles by the atomizing effect of high velocity gases, or itmay be a combination of such materials.

The invention claimed is:

1. A fluid energy mill comprising an inlet section, a classificationsection, an upstack section connecting one end of said inlet section toone end of the classification section, and a downstack sectionconnecting the other end of said inlet section to the other end of theclassification section, tangentially arranged nozzles leading into saidinlet section from a source of gaseous fluid under pressure, a feedinlet leading into said inlet section for inserting raw material intosaid mill, at least one exhaust outlet in said classification section,said exhaust outlet being adjacent the inner periphery of thecentrifugal path of particles and fluid being propelled through saidmill, and said inlet section and upstack section having a continuoustractrix antifriction longitudinal curvature.

2. The mill of claim 1 wherein said classification section is generallycircular and said exhaust outlet is positioned in the center thereof.

Hum" 11A 3. The mill of claim 2 wherein there are two exhaust outlets,one at each side of said classification section.

4. The mill of claim 2 wherein said exhaust outlet comprises anopen-ended tube extending transversely through said classificationsection, said tube having a slot therein which is in communication withthe interior of said classification section.

5. The mill of claim 1 wherein said classification section islongitudinally arcuate and wherein the exhaust outlet is adjacent thesaid other end of the classification section.

6. The mill of claim 1 wherein inclined nozzles, connected to a sourceof gaseous fluid under pressure, lead into said classification section.

7. A method of treating pulverulent material in a mill which comprisespropelling the particles of said material through an inlet zone, whereinthey are entrained in and acted on by gaseous fluid injected into saidinlet zone in directions that are tangential to the initial path of saidparticles, passing the resultant particles from said inlet zone througha curved path which is defined by a tractrix antifriction curvature, andthen passing the particles through a classification zone which isdefined at least partially by a continuation of said tractrix curvature,said particles being separated into heavier and lighter particles withinsaid classification zone, and said lighter particles being passedthrough an exhaust outlet from said classification zone.

8. The method of claim 7 wherein the classification zone forms anelliptical path in which the heavier particles are centrifugally held onthe outer periphery of said path while the lighter particles arecentrifugally held on the inner periphery of said path, said lighterparticles being exhausted from said inner periphery.

9. The method of claim 7 wherein additional gaseous fluid is injectedinto said classification zone in a direction to accelerate the movementof the lighter particles.

2. The mill of claim 1 wherein said classification section is generallycircular and said exhaust outlet is positioned in the center thereof. 3.The mill of claim 2 wherein there are two exhaust outlets, one at eachside of said classification section.
 4. The mill of claim 2 wherein saidexhaust outlet comprises an open-ended tube extending transverselythrough said classification section, said tube having a slot thereinwhich is in communication with the interior of said classificationsection.
 5. The mill of claim 1 wherein said classification section islongitudinally arcuate and wherein the exhaust outlet is adjacent thesaid other end of the classification section.
 6. The mill of claim 1wherein inclined nozzles, connected to a source of gaseous fluid underpressure, lead into said classification section.
 7. A method of treatingpulverulent material in a mill which comprises propelling the particlesof said material through an inlet zone, wherein they are entrained inand acted on by gaseous fluid injected into said inlet zone indirections that are tangential to the initial path of said particles,passing the resultant particles from said inlet zone through a curvedpath which is defined by a tractrix antifriction curvature, and thenpassing the particles through a classification zone which is defined atleast partially by a continuation of said tractrix curvature, saidparticles being separated into heavier and lighter particles within saidclassification zone, and said lighter particles being passed through anexhaust outlet from said classification zone.
 8. The method of claim 7wherein the classification zone forms an elliptical path in which theheavier particles are centrifugally held on the outer periphery of saidpath while the lighter particles are centrifugally held on the innerperiphery of said path, said lighter particles being exhausted from saidinner periphery.
 9. The method of claim 7 wherein additional gaseousfluid is injected into said classification zone in a direction toaccelerate the movement of the lighter particles.